1. Field of the Invention
The present invention relates to an image reproducing apparatus and an image reproducing method for improving the controllability of an AV (Audio Visual) server or the like for recording/reproducing image data in reproducing image data.
2. Description of the Related Art
The demand for reproducing a plurality of image and audio data simultaneously from one recording/reproducing apparatus, differing from a conventional VTR (Video Tape Recorder), is growing with the late progress of multi-channelization in providing information due to the dissemination of CATV. (Cable Television) and the like. Then, in order to meet with this demand, an apparatus called an AV server (or a video server) for recording/reproducing image and audio data by using randomly accessible recording media such as a hard disk is now spreading.
For instance, an AV server installed in a broadcasting station is required to have a high data transfer rate in order to keep image and sound quality at certain level or more. It is also required to be able to record a large amount of data in order to broadcast for a long period of time and to have high reliability so as not to interrupt the broadcasting.
Then, the AV server is arranged so as to be able to increase the data transfer rate and the storage capacity by using a recording/reproducing apparatus containing a plurality of HDDs (Hard Disk Drives) which can be operated in parallel and to be able to assure the reliability, even if either one HDD happens to malfunctions, by restoring data by recording parity data.
By the way, an AV server called a multi-channel AV server which can accommodate to various use modes has come to be realized lately to be used in sending a plurality of recorded material data simultaneously through multi-channels or in constructing an NVOD (Near Video On Demand) system for reproducing the same material data through multi-channels by shifting reproducing time.
Technology of RAID (Redundant Arrays of Inexpensive Disks) which was advocated in a paper presented by Patterson et. al., in 1988 (Patterson, D. A., Gibson, G., Kats, R. H., xe2x80x9cA Case for Redundant Arrays of Inexpensive Disk (RAID)xe2x80x9d ACM SIGMOD Conference, Chicago, III., Jun. 1-3, 1988) is used in the recording/reproducing apparatus used in such multi-channel AV server. While RAID is categorized into five RAID-1 through RAID-5 in the paper, the typical ones are RAID-1, RAID-3 and RAID-5. It is noted although there is a category of RAID-0 as a category in terms of the explanation, it is a mode for operating a plurality of hard disks in parallel.
The RAID-1 is a mode of writing the same contents in two hard disks and the RAID-3 is a mode of recording input data in a plurality of HDDs by dividing it into data of certain length and of generating and writing parity data into another one HDD. The RAID-5 is a mode of recording one divisional data in one HDD as data block by dividing the data into large unit (block), of recording the result of an exclusive logical sum of the data blocks in each HDD corresponding to each other into another HDD as parity block (parity data) and of distributing the parity block to the whole HDDs.
FIG. 1 shows one exemplary structure of the conventional AV server system (the system means one in which a plurality of units are collected logically and it does not matter whether the respective units are stored in one case or not) using the RAID technology.
This AV server system comprises a multi-channel AV server 100 which is capable of providing multi-input/output of a plurality of image data (audio data will be included in image data as necessary hereinafter) and may be utilized as a system for broadcasting CMs (commercial) and news.
The multi-channel AV server 100 comprises a plurality of disk array units 1101 through 1104 for recording input image data and a processor 120. It is noted that the processor 120 is configured so as to control the input of the image data to be recorded in the disk array units 1101 through 1104 and to control the output of the image data reproduced from the disk array units 1101 through 1104.
Then, the multi-channel AV server 100 records respective ones of a plurality of input image data DI1 through IN (N is an integer value greater than 2) inputted from a VTR 121 for reproducing images and a parabola antenna 122 for receiving data via a satellite line at least in one of the disk array units 1101 through 1104. The multi-channel AV server 100 also reproduces data recorded in the disk array units 1101 through 1104 as necessary and outputs as output data Do1 through NoN to the monitor 123 and the parabola antenna 124 for example.
FIG. 2 shows one exemplary structure of the disk array unit 110i (here, i=1, 2, 3 and 4) in FIG. 1.
The disk array unit 110i comprises a plurality of, e.g., five, HDDs 1311 through 1315 and a disk array controller 130 for controlling those 13115. In the disk array unit 110i, data is read/written from/to the HDDs 1311 through 1315 per predetermined unit (in unit of one frame or one GOP (Group of Picture) for example). While the mode for writing/reading data to/from the plurality of HDDs is the mode called RAID-0, one out of the plurality of HDDs is used for recording the parity data and the remaining HDDs are used for recording the image data in the RAID-3 for example.
It is noted that although the five HDDs 1311 through 1315 are shown in FIG. 2, the number of HDDs composing the disk array unit 110i is not limited to that number.
Data of one frame is divided in unit of one byte for example in the 130 in the disk array unit 110i and the divided data is written to the HDDs 1311 through 1315 in parallel. The 110i also reproduces data recorded in the HDDs 1311 through 1315 and outputs the reproduced respective data by multiplexing into the same condition with that at the time of input.
Here, first frame data F1 and second frame data F2 are written to the HDDs 1311 through 1315 in parallel in FIG. 2.
It is noted that in order to reduce the influence of seek (retrieving operation) time of data in the HDDs. 1311 through 1315, image data is written/read in a certain degree of lump, e.g., several tens frames) at one time of access.
By the way, it is required to reproduce the recorded data at variable speed in structuring an editing system for example by using the multi-channel AV server 100 as described above. That is, the variable speed reproduction is often used in editing works and the like because it is convenient in finding a specific scene for example.
As a method for implementing the variable-speed reproduction in the multi-channel AV server 100, there has been one of reading image data by culling frames in correspondence to it reproducing speed. However, setting aside the case of the RAID-5 in which image data of one frame is recorded in one HDD in reading image data by culling the frames, there has been a case in which image data necessary for variable-speed reproduction of desired speed cannot be read in the RAID-0 and RAID-3 in which image data of one frame is recorded across the plurality of HDDS.
That is, because image data has been recorded into the plurality of HDDs without controlling the recording pattern specifically in the past, the image data of one frame is distributed into the plurality of HDDs and is-recorded in parallel in the order of line scan (in the order of coding in case when image data is coded) in RAID-0 and RAID-3. Accordingly, although the continuous frames may be reproduced by seeking image data of the first frame and then by reading the image data continuously in each HDD, image data of certain frame must be sought every time when the image data of frame to be read changes in each HDD in reproducing sporadic frames. Because it takes about 10 to 20 mil-seconds in seeking data in the HDD, the performance would be about 3 frames/100 msec for example as data reading speed when data must be sought every time when image data of a frame to be read changes. As a result, the multi-channel AV server 100 whose basic function is multi-accessing can output data only by the performance of several frames/sec and it becomes difficult to read data of 30 frames/sec which is normally required.
Further, a fall of original image (so-called missing frame) occurs in a reproduced image when image data is read by culling frames.
That is, while jumped data of frames F1, F3, F5, F7, F9, . . . is read in reproducing continuous image data of frames F1, F2, F3, . . . at double speed, the frames F2, F4, F6, F8, . . . fall in the reproduced image. While the data of the frames F1, F5, F9, . . . is outputted in reproducing the image at quadruple-speed, the more original images fall as compared to the case of double-speed reproduction. The fall of the image increases as the reproducing speed increases.
Because the variable-speed reproduction is used often in seeking a specific scene in editing works as described above, it becomes difficult to find a frame representing an instant image like a frame showing a scene of lighting a flashbulb when the fall of frames occurs in reproducing at variable speed, thus affecting the editing works.
Then, the applicant of the present invention has proposed a method of minimizing the fall of frames and of shortening the seek time by recording image data to a plurality of HDDs while controlling its recording pattern and by reading image data for, so to speak, each reproducing speed corresponding to the reproducing speed of the variable-speed reproduction from the plurality of HDDs in Japanese Patent Application No. Hei. 10-122535 for example.
By the way, according to the method proposed in Patent Application No. Hei. 10-122535, the image data of the reproducing speed is read from the HDDs corresponding to the reproducing speed of the variable-speed reproduction, so that when a control is made so as to change the reproducing speed, that image data for the reproducing speed after the change must be read from the HDD.
However, the multi-channel AV server is configured so as to periodically assign a time accessible to a plurality of disk array units (hereinbelow, called as a time slot as necessary) to each channel in general and each channel is allowed to access to the disk array unit in the time slot assigned to it (hereinbelow, called as own time slot as necessary). Then, because the time slot is given to each channel periodically as described above, the more the number of channels, the longer the interval by which each channel can access to the disk array unit, i.e., the time until when accessing to the next disk array unit after accessing the disk array unit (hereinbelow called as a time slot period) becomes.
When the number of channels increases the time slot period is prolonged as described above. Accordingly, when a control is made so as to change the reproducing speed, it takes time to read the image data for reproducing speed corresponding to that control and as a result, a considerable time-lag occurs until when the reproducing speed changes actually from when the control has been made. The slow reaction of the unit to the control causes the user to feel that the controllability is bad and as a result, it drops the efficiency of the editing works.
The present invention has been made in view of the above-mentioned circumstances and improves the controllability in reproducing image data.
According to the invention, an image reproducing apparatus comprises reading means for reading divisional data of part corresponding to requested reproducing speed from a plurality of groups of recording media when a reproduction of images is requested; storage means for storing the divisional data read from the plurality of groups of recording media; structuring means for structuring the reproduced image by reading and using the divisional data stored in the storage means; and control means for controlling a reading pattern of the divisional data from the storage means.
According to the invention, an image reproducing method comprises a reading step for reading divisional data of part corresponding to requested reproducing speed from a plurality of groups of recording media when a reproduction of images is requested; a storing step for storing the divisional data read from the plurality of groups of recording media; a structuring step for structuring the reproduced image by reading and using the divisional data stored in the storage means; and a controlling step for controlling a reading pattern of the divisional data from the storage means.
According to the image reproducing apparatus and the image reproducing method constructed as described above, the divisional data of the part corresponding to the requested reproducing speed is read from the respective ones of the plurality of groups of recording media and is stored in the storage means when the reproduction of image is requested. The reproduced image is structured by reading the divisional data stored in the storage means and by using the divisional data. In such case, the divisional data reading pattern from the storage means is controlled.
The specific nature of the invention, as well as other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawings.